Design-of-experiment strategy for the production of mannanase biocatalysts using plam karnel cake and its application to degrade locust bean and guar gum

Production of β-mannanase from thermotolerant Aspergillus terreus FBCC 1369 was optimized by response surface methodology (RSM) using plam kernel cake (PKC) as substrate. Effect of particle size of substrate, pH, moisture content and carbon and nitrogen supplements was studied. Under unoptimized conditions i.e. 2 mm particle size of PKC, moisture level 1:1 and pH 6.5 fungus produced only 41 U/gds. Initial optimum conditions i.e. 0.5 particle size of PKC, locust bean gum (1% w/v) and urea (1% w/v) at pH 6.5 and moisture level 1:1 resulted in 159 U/gds of β-mannanase yield. The effect of pH and moisture content on production was further optimized using RSM. Rotatable central composite design (RCCD) was employed to investigate the effects of pH (4-10) and moisture content (5-20 ml) on mannanase yield during solid state fermentation (SSF). Results revealed statistical significance of model as evidenced from high value of coefficient of determination (R2=1.000) and P<0.05. Optimized medium consisted of 5 g PKC of 0.5 particle size, LBG 1% (w/v) and urea 1% (w/v) as carbon and nitrogen supplementation with 12.8 ml moisture content and pH 8.0 resulting in 417 U/gds β-mannanase, which was 10- fold higher than the original value. The β-mannanase production obtained in this study using A. terreus was significantly higher than those reported in the literature. Activity of accessory enzymes, α-galactosidase (13 U/gds) and β-glucosidase (21 U/gds) in this preparation indicated that it can be used to achieve complete hydrolysis of galactoglucomannan by synergistic action of these enzymes. The end product analysis of mannanolytic action analyzed using HPLC revealed formation of mannose and mannobiose from galactomannan (locust bean and guar gum).